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Parsing, Compiling and Static Metaprogramming Patrick Dubroy Google Munich @dubroy

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Writing programs that manipulate programs as data Metaprogramming

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Static Metaprogramming Writing programs that manipulate code

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COMPILER

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COMPILER Code Code

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COMPILER C++ 1011

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C++ 1011 PARSER CODEGEN Parse Tree

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Esprima A high-performance JavaScript parser written in JavaScript. Also: estraverse & escodegen

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var esprima = require('esprima'); esprima.parse(" \ function getAnswer() { \ return 42; \ } \ ");

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Program FunctionDeclaration Identifier Body ReturnStatement Literal “42”

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{ "type": "Program", "body": [ { "type": "FunctionDeclaration", "id": { "type": "Identifier", "name": "getAnswer" }, "params": [], "defaults": [], "body": { "type": "BlockStatement", "body": [ { "type": "ReturnStatement", "argument": { "type": "Literal", "value": 42, "raw": "42" } } ] }, } ] }

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function checkStyle(code, filename) { var ast = esprima.parse(code, parseOptions); var errors = []; estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'VariableDeclaration') checkVariableNames(node, errors); } }); return formatErrors(code, errors, filename); } function checkVariableNames(node, errors) { _.each(node.declarations, function(decl) { if (decl.id.name.indexOf('_') >= 0) { return errors.push({ location: decl.loc, message: 'Use camelCase, not hacker_style!' }); } }); }

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function checkStyle(code, filename) { var ast = esprima.parse(code, parseOptions); var errors = []; estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'VariableDeclaration') checkVariableNames(node, errors); } }); return formatErrors(code, errors, filename); } function checkVariableNames(node, errors) { _.each(node.declarations, function(decl) { if (decl.id.name.indexOf('_') >= 0) { return errors.push({ location: decl.loc, message: 'Use camelCase, not hacker_style!' }); } }); } var ast = esprima.parse(code, parseOptions);

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function checkStyle(code, filename) { var ast = esprima.parse(code, parseOptions); var errors = []; estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'VariableDeclaration') checkVariableNames(node, errors); } }); return formatErrors(code, errors, filename); } function checkVariableNames(node, errors) { _.each(node.declarations, function(decl) { if (decl.id.name.indexOf('_') >= 0) { return errors.push({ location: decl.loc, message: 'Use camelCase, not hacker_style!' }); } }); } estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'VariableDeclaration') checkVariableNames(node, errors); } });

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function checkStyle(code, filename) { var ast = esprima.parse(code, parseOptions); var errors = []; estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'VariableDeclaration') checkVariableNames(node, errors); } }); return formatErrors(code, errors, filename); } function checkVariableNames(node, errors) { _.each(node.declarations, function(decl) { if (decl.id.name.indexOf('_') >= 0) { return errors.push({ location: decl.loc, message: 'Use camelCase, not hacker_style!' }); } }); } function checkVariableNames(node, errors) { _.each(node.declarations, function(decl) { if (decl.id.name.indexOf('_') >= 0) { return errors.push({ location: decl.loc, message: 'Use camelCase, not hacker_style!' }); } }); }

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function checkStyle(code, filename) { var ast = esprima.parse(code, parseOptions); var errors = []; estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'VariableDeclaration') checkVariableNames(node, errors); } }); return formatErrors(code, errors, filename); } function checkVariableNames(node, errors) { _.each(node.declarations, function(decl) { if (decl.id.name.indexOf('_') >= 0) { return errors.push({ location: decl.loc, message: 'Use camelCase, not hacker_style!' }); } }); }

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var foo = bar; var this_is_bad = 3; function blah() { return function x() { var oops_another_one; } }

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var foo = bar; var this_is_bad = 3; function blah() { return function x() { var oops_another_one; } } [ 'Line 1, column 34: Use camelCase for variable names, not hacker_style.', 'Line 1, column 119: Use camelCase for variable names, not hacker_style.' ]

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function addLogging(code) { var ast = esprima.parse(code); estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } }); return escodegen.generate(ast); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); }

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function addLogging(code) { var ast = esprima.parse(code); estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } }); return escodegen.generate(ast); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); } var ast = esprima.parse(code);

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function addLogging(code) { var ast = esprima.parse(code); estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } }); return escodegen.generate(ast); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); } estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } });

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function addLogging(code) { var ast = esprima.parse(code); estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } }); return escodegen.generate(ast); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); }

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FunctionDeclaration Identifier BlockStatement Statement Statement ... Array .body .body

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FunctionDeclaration Identifier BlockStatement Statement Statement ... Array .body .body Statement

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FunctionDeclaration Identifier BlockStatement Statement Statement ... Array .body .body Statement

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function addLogging(code) { var ast = esprima.parse(code); estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } }); return escodegen.generate(ast); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); } return escodegen.generate(ast);

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function addLogging(code) { var ast = esprima.parse(code); estraverse.traverse(ast, { enter: function(node, parent) { if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') { addBeforeCode(node); } } }); return escodegen.generate(ast); } function addBeforeCode(node) { var name = node.id ? node.id.name : ''; var beforeCode = "console.log('Entering " + name + "()');"; var beforeNodes = esprima.parse(beforeCode).body; node.body.body = beforeNodes.concat(node.body.body); }

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addLogging(" \ function foo(a, b) { \ var x = 'blah'; \ var y = (function () { \ return 3; \ })(); \ } \ foo(1, 'wut', 3); \ ");

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addLogging(" \ function foo(a, b) { \ var x = 'blah'; \ var y = (function () { \ return 3; \ })(); \ } \ foo(1, 'wut', 3); \ "); function foo(a, b) { console.log('Entering foo()'); var x = 'blah'; var y = function () { console.log('Entering ()'); return 3; }(); } foo(1, 'wut', 3);

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addLogging(" \ function foo(a, b) { \ var x = 'blah'; \ var y = (function () { \ return 3; \ })(); \ } \ foo(1, 'wut', 3); \ "); function foo(a, b) { console.log('Entering foo()'); var x = 'blah'; var y = function () { console.log('Entering ()'); return 3; }(); } foo(1, 'wut', 3);

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Parser Generators

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PARSER GENERATOR Language Grammar Parser

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No content

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Formal Grammars

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expr → expr [-+] term | term term → term [*/] factor | factor factor → '(' expr ')' | number number → [0-9]+ Context-Free Grammar

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expr ::= expr [-+] term | term term ::= term [*/] factor | factor factor ::= '(' expr ')' | number number ::= [0-9]+ Backus–Naur Form

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expr = expr [-+] term | term term = term [*/] factor | factor factor = '(' expr ')' | number number = [0-9]+ EBNF

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expr = expr [-+] term | term term = term [*/] factor | factor factor = '(' expr ')' | number number = [0-9]+ | | | CFG: Unordered choice

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expr = expr [-+] term / term term = term [*/] factor / factor factor = '(' expr ')' / number number = [0-9]+ / / / PEG: Ordered Choice

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var PEG = require('pegjs'); var parser = PEG.buildParser(" \ expr = expr [-+] term / term \ term = term [*/] factor / factor \ factor = '(' expr ')' / number \ number = [0-9]+ \ "); parser.parse('1+10');

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var PEG = require('pegjs'); var parser = PEG.buildParser(" \ expr = expr [-+] term / term \ term = term [*/] factor / factor \ factor = '(' expr ')' / number \ number = [0-9]+ \ "); parser.parse('1+10'); ~/node_modules/pegjs/lib/peg.js:3316 throw new PEG.GrammarError( ^ PEG.GrammarError: Left recursion detected for rule "expr".

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expr = expr [-+] term / term term = term [*/] factor / factor factor = '(' expr ')' / number number = [0-9]+ Left Recursion

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = [0-9]+ Left Recursion

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var PEG = require('pegjs'); var parser = PEG.buildParser(" \ expr = term ([-+] term)* \ term = factor ([*/] factor)* \ factor = '(' expr ')' / number \ number = [0-9]+ \ "); parser.parse('1+10');

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var PEG = require('pegjs'); var parser = PEG.buildParser(" \ expr = term ([-+] term)* \ term = factor ([*/] factor)* \ factor = '(' expr ')' / number \ number = [0-9]+ \ "); parser.parse('1+10'); [[["1"],[]],[["+",[["1","0"],[]]]]]

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = [0-9]+ Semantic Actions

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ Semantic Actions

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); } Semantic Actions

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); } Semantic Actions [["1",[]],[["+",["10",[]]]]]

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); } Semantic Actions [["1",[]],[["+",["10",[]]]]] "10"

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); }

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{ function Number(digits) { this.nodeType = 'Number'; this.value = digits.join(''); } ... } expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); }

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{ function Number(digits) { this.nodeType = 'Number'; this.value = digits.join(''); } ... } expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); }

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{ function Number(digits) { this.nodeType = 'Number'; this.value = digits.join(''); } ... } expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return new Number(digits); }

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An AltJS Language in 5 minutes

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expr = term ([-+] term)* term = factor ([*/] factor)* factor = '(' expr ')' / number number = digits:[0-9]+ { return digits.join(''); }

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expr = term ([-+] term)*

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expr = term ([-+] term)* / decl

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expr = term ([-+] term)* / decl decl = ident ' := ' expr

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+ digit = [0-9]

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] program = expr? ('.' [ \\n]* expr)*

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] program = expr? ('.' [ \\n]* expr)* > parser.parse('x := 2+5. y := 3')

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] program = expr? ('.' [ \\n]* expr)* > parser.parse('x := 2+5. y := 3') [[["x"]," := ",[["2",[]],[["+",["5",[]]]]]],[[".",[], [["y"]," := ",[["3",[]],[]]]]]]

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expr = term ([-+] term)* / decl decl = ident ' := ' expr ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] program = expr? ('.' [ \\n]* expr)*

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program = expr? ('.' [ \\n]* expr)* expr = term ([-+] term)* / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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program = expr? ('.' [ \\n]* expr)* expr = term ([-+] term)* / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; }

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program = expr? ('.' [ \\n]* expr)* expr = term ([-+] term)* / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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program = expr? ('.' [ \\n]* expr)* expr = term ([-+] term)* / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] > parser.parse('x := 2+5. y := 3')

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program = expr? ('.' [ \\n]* expr)* expr = term ([-+] term)* / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] > parser.parse('x := 2+5. y := 3') ["var x = 2,,+,5,;",[[".",[],"var y = 3,,;"]]]

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program = expr? ('.' [ \\n]* expr)* expr = term ([-+] term)* / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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program = expr? ('.' [ \\n]* expr)* expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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program = expr? ('.' [ \\n]* expr)* expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] > parser.parse('x := 2+5. y := 3')

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program = expr? ('.' [ \\n]* expr)* expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] > parser.parse('x := 2+5. y := 3') ["var x = 2+5;",[[".",[],"var y = 3;"]]]

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program = expr? ('.' [ \\n]* expr)* expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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program = e:expr? rest:(('.' [\\n ]* e:expr){ return e; })* { return [e].concat(rest).join('\n'); } expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z]

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program = e:expr? rest:(('.' [\\n ]* e:expr){ return e; })* { return [e].concat(rest).join('\n'); } expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] > parser.parse('x := 2+5. y := 3')

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program = e:expr? rest:(('.' [\\n ]* e:expr){ return e; })* { return [e].concat(rest).join('\n'); } expr = t:term rest:([-+] term)* { return flatten(t.concat(rest)); } / decl decl = id:ident ' := ' e:expr { return 'var ' + id + ' = ' + e.join('') + ';'; } ident = (digit / letter / '_')+ digit = [0-9] letter = [a-zA-Z] > parser.parse('x := 2+5. y := 3') var x = 2+5; var y = 3;

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Resources github.com/pdubroy/jsconfeu-talk Slides: goo.gl/qs4Gna Esprima: esprima.org PEG.js: pegjs.majda.cz

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Danke!